高斯脉冲冷却机械振子  

Cooling the mechanical resonator by Gaussian pulses

作　　者：陈志心 林青[1] CHEN ZhiXin;LIN Qing(Fujian Key Laboratory of Light Propagation and Transformation,College of Information Science and Engineering,Huaqiao University,Xiamen 361021,China)

机构地区：[1]华侨大学厦门校区信息科学与工程学院福建省光传输与变换重点实验室

出　　处：《中国科学：物理学、力学、天文学》2020年第3期138-148,共11页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：国家自然科学基金(编号:11574093,11404117);福建省自然科学基金(编号:2017J01004);华侨大学中青年科技支持计划(编号:ZQN-PY113)资助项目

摘　　要：光力学系统常被用来实现机械振子的基态冷却,进而实现宏观量子态制备.如何获得更好的冷却效果是光力冷却的核心问题.然而理论证明,采用单束连续光来驱动机械振子存在冷却极限,即无法通过提高驱动强度或振子频率来获得更低的冷却比率,因而需要发展新的动力学理论.我们探讨采用高斯脉冲来驱动机械振子,这一光力学系统在绝大多数情况下不存在稳态,无法使用常用的线性化展开来处理.我们采用新的线性化方法获得有效哈密顿量,由此可以获得光力学系统的动力学演化,进而直接得到系统热声子数的变化.通过详细分析脉冲波形、脉冲强度以及脉冲宽度对热声子数演化的影响,证明选择合适的驱动强度、脉冲宽度,机械振子可以被单个脉冲冷却到基态,并通过多个脉冲来保持在基态.甚至利用脉冲波形中驱动强度的增、减,可以延缓压缩效应对光力系统造成的加热.由此可以突破单束连续驱动的冷却极限,甚至通过强、短高斯脉冲可以将冷却极限降低1/2,展现出脉冲驱动冷却光力学系统的优势.The optomechanical system has been widely used to realize the quantum ground state cooling of mechanical resonator,which is the way to create macroscopic quantum state.How to get the better cooling effect is evidently the central point.However,it has been demonstrated that there is a cooling limit if using only one single continuous-wave pump to drive the mechanical resonator,i.e.,the cooling rate cannot be decreased by increasing the drive intensity or the mechanical frequency,so that the new dynamics should be developed.Here we present an approach to cool the mechanical resonator by the Gaussian pulses.For the pulsed optomechanical system,the common steady-state expansion approach is not available,since no steady state can be found in most cases.We use the new linearized approach to get the effective Hamiltonian and the dynamical evolution of the optomechanical system,with which the thermal phonon number of the mechanical resonator can be achieved directly.After investigating how the pulse profile,drive intensity and pulse duration affect the evolution of thermal phonon number in details,we show that the mechanical resonator can be well cooled down to the ground state by a single pulse,and can be well preserved by the multiple pulses,with the appreciated drive intensity,duration.Moreover,the character of drive intensity increasing and decreasing of the pulse profile,enables one to delay the squeezing effect which results in the heating of the mechanical resonator.As a result,the cooling limit of single continuous-wave driven optomechanical system can be broken by the pulsed optomechanical system.Even the half of the cooling limit of the continuous optomechanical system can be achieved by the short and strong Gaussian pulses,which is the main advantage of the ground state cooling by pulse drives.

关 键 词：光力学系统 基态冷却 高斯脉冲 

分 类 号：O413.1[理学—理论物理]